A modern aircraft can include a large array of onboard computers including flight, navigation and communications systems among others. Often, such systems are networked together to permit integration of all subsystems on the aircraft. A communications databus is often used to provide the channel or signal pathway for the various systems of the aircraft.
As aircraft continue to become more complex, the need to ensure reliable and timely delivery of critical data to the flight crew creates design challenges and an emerging need for classifying flight data according to priority and data type. Often, multiple systems may be attempting to communicate over the same databus at the same time. Bandwidth, however, is limited and sharing of the communications topology by all systems on the aircraft is necessary, Accordingly, data transmissions on the bus are often relayed from one system to another according to timing and availability of bandwidth on the communications databus.
Over the years, various data formats that describe the timing and sequence of different types of data have evolved. These include periodic or deterministic data which is communicated according to predetermined timing sequences and cycles and aperiodic data, such as isochronous and asynchronous data. At the same time, data transmission protocols that standardize and dictate how such data formats are communicated between systems in an aircraft are available. Such protocols include the ARINC 629 standard and ASCB versions A–C.
With the ARINC 629 standard, data transmissions alternate between periodic and aperiodic data intervals. Terminals have one periodic transmission per frame, and may get one aperiodic transmission if time is remaining after the periodic transmission. Another prior art protocol includes ControlNet, a protocol for industrial automation where periodic data is sent first, then aperiodic data is sent using a token-passing mechanism.
A limitation of prior art protocols is that some require negotiation between the transmitter and receiver systems to ensure that data arrives at its intended destination point. Such negotiation sessions consume valuable bandwidth on the communications databus and add latency to the overall system. In addition bandwidth can depend on the number of systems accessing the databus so that a particular file may not receive the bandwidth necessary to reach its intended destination. In some circumstances, the system receives no guarantee of any bandwidth no assurances that a file was actually received. This is unacceptable in an avionics environment where data can be critical and receipt by flight crew personnel must be assured with guaranteed bandwidth assigned to critical data for safe and reliable operation of the aircraft.
In particular, various modules in an aircraft compete with one another for transmission time on the communications databus. The databus provides the signaling pathways along which periodic and aperiodic data is transmitted from one system to another on the aircraft. A problem with existing databus transmission protocols is that the systems are not able to adequately allocate bandwidth for transmission of the most important aperiodic data from aircraft systems or modules. The result is that transmission of data between modules fails, is delayed, or is transmitted inefficiently, with low-priority data being sent before high-priority data.
What is needed is a communications protocol for use in an avionics environment where available bandwidth is partitioned according to priority and whether the data transmission is periodic or aperiodic. A method and system of prioritizing aperiodic data transmission requests from the various systems in the aircraft, and transmit the aperiodic data based on the order determined by the prioritization scheme would provide numerous advantages over the prior art.